Page 30: of Maritime Reporter Magazine (March 2018)

of critical components at sea can result in be eliminated completely, it can be man- Corrosion of Structural Elements be controlled but it is not easily elimi- the loss of life or the sinking of a vessel; aged to such a degree that catastrophic The trend towards autonomous vessels nated.

or necessitate costly rescue operations. failures decrease. will have consequences for the manage- Ships are operated in a brutally corro-

The challenge now is to include cor- The need to further minimize mari- ment of corrosion. Maritime corrosion is sive environment, with ship hulls espe- rosion prevention in the design and con- time corrosion on autonomous ships can a subject that requires aggressive, proac- cially prone to corrosion. The biofouling struction of autonomous ships and their be taken as an opportunity to improve tive measures. Special alloys, coatings of the hulls can contribute to drag and onboard sensors and computing systems. systems for monitoring and controlling and sacri? cial anodes have been devel- add to fuel costs. Ships carrying freight

This will not be a subtle change and maritime corrosion. This article brie? y oped to slow down the inevitable dete- on long voyages need reliable, long last- could necessitate a holistic look at how reviews a few of the ways that current rioration of materials that occurs in salt ing coatings. ships are constructed. An autonomous knowledge of maritime corrosion can be water environments. It is rarely a ques- The days when ships were free to over- ship cannot depend upon crew members adopted in the development of autono- tion of “if” but more often a question of look the issue of corrosion are gone. Bal- to monitor coating performance and ad- mous shipping. “when.” Furthermore, corrosion can be last and cargo tanks need to be coated. dress its maintenance at sea. A ship that unpredictable and catastrophic. Risk can This is a class requirement. If these has not been maintained, coating-wise, coatings are not “good” according to the for six months will deteriorate dramati- class, the ship cannot trade. cally. Ships must be built to a higher There are several approaches to man- standard of corrosion resistance at ev- aging corrosion of a ship’s hull. Most of ery level before they are commissioned. these involve predicting the time to fail-

Once in the water, they must be regularly ure. The ship’s hull itself can be made of inspected and monitored and held to a special materials selected for their cor- higher standard than a manned vessel. rosion resistance, although, practically

Otherwise the failure of a relatively mi- speaking, no material is completely safe nor part that normally would be repaired from marine corrosion. That said, com- at sea could result in a costly rescue op- posites – such as glass ? ake epoxy – pro- eration to recover a vessel stranded at vide excellent corrosion resistance. This sea. underutilized technology – suitable for

We are now learning the downstream use in hand rails, ladders, pipe supports effects of Tier II engine modi? cations, and cable trays – has been available including increased cold corrosion in for more than 20 years, but resistance long stroke and more ef? cient engines. to change is strong in the ship building

New issues may come into play with community.

Tier III engines, which could include For autonomous shipping, monitoring complex additions such as Exhaust Gas the condition of the hull is especially

Recirculation (EGR), Selective Catalytic important, as daily monitoring by the

Reduction (SCR) and even scrubbers. crew and the potential for early interven-

The Ballast Water Treatment Systems tion will be nonexistent. The use of un- (BWTS) imposed on shipping, as de- manned aerial systems for surveys may veloped in the past decade, are proving not be practical when launched from the to be quite maintenance intensive and autonomous vessel itself with no crew would require people onboard. aboard. Autonomous underwater ve-

The fuel situation through 2020 is al- hicles and remotely operated vehicles ready uncertain, and beyond 2020 it is possess unique capabilities that could even more so. The one certainty is that be developed for inspecting ship hulls each major change will have down- at sea. The key here is the prediction of stream consequences. the time to failure or the detection of a

Fortunately, corrosion is better under- potentially catastrophic condition that stood today compared to the past. Un- would require bringing the ship into a fortunately, such knowledge is generally port for emergency repair.

not employed; at best, corrosion control Another solution is to embed sensors is not applied as effectively as it could within the hull, such as stress sensors or be, considering the excess focus on con- ultrasonic measuring instruments. The struction costs rather than long-term vi- processing of such signals can indicate ability and corrosion protection. a condition of biofouling or rusting; or

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Many superior products and solutions even a combination of both.

“ on the market today are not used because As is usually the case, there are trad- they are not easily adjusted into the cost- eoffs between the costs for monitoring

The challenge now is to include corrosion pre- focused construction process. The ? nan- and maintaining the hull. Risk manage- vention in the design and construction of au- cial cost of the vessel is the second most ment will require a corrosion expert to important cost in shipping behind fuel evaluate the data. This knowledge could tonomous ships and their onboard sensors costs. Sophisticated corrosion preven- be built into the autonomous ship’s and computing systems. This will not be a tion solutions drive up costs, and these knowledge base, or judgment calls can subtle change and could necessitate a ho- added costs could become higher than be made by a corrosion expert who is re- listic look at how ships are constructed. the cost of crew members. motely monitoring the ship’s condition.

New alloys and coatings now exist that Risk management could affect the size

An autonomous ship cannot depend upon crew greatly extend the useful life of com- of the vessel; it may be more practical to members to monitor coating performance.

ponents, particularly at sea. Improved carry cargo on many small ships and so methods for monitoring corrosion can distribute the risk. be employed. While corrosion cannot 30 Maritime Reporter & Engineering News • MARCH 2018

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